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The Basking Shark

By Bonnie J. Cardone

The Basking Shark (Cetorhinus maximus) belongs to an extremely interesting order, Lamniformes, the Mackerel Sharks. Its cousins include Great White, Mako, Megamouth, Goblin, Thresher, Sand Tiger and Crocodile Sharks. What this seemingly diverse collection of fishes has in common includes a cylindrical trunk, conical or cylindrical head, five pairs of gill slits, small spiracles, barbeless nostrils, no nictitating membrane on the lower eyelid and two spineless dorsal fins. Most Lamniformes are as distinctive (and odd) looking as the participants in a Halloween parade. The huge Megamouth, for instance, has an incredible mouth. Goblin Sharks have weird, dagger-like snouts. Thresher Sharks have an exceptionally long upper tail lobe. Sand Tiger and Mako Sharks have mouths filled with snaggly teeth. Crocodile Sharks have huge eyes.

No less odd than its relatives is the Basking Shark. If one happened to be coming at you with its mouth open, you would have no trouble identifying it. No shark has a larger, more distinctive mouth; fully opened it is diamond shaped and absolutely cavernous. The mouth is also notable for its lack of big sharp teeth. The Basking Shark is a harmless plankton feeder with only minute hooked teeth. It is the second largest elasmobranch; only the Whale Shark is larger.

The two features mentioned above are not the only ones that distinguish the Basking Shark. It has a small, pointed head and 'enormous gill slits that virtually incircle the head.' (The FAO Species Catalogue: Sharks of the World.) The shark also has unusual skin. The FAO Species Catalogue notes: 'Divers should avoid contact with the skin of this shark, which has large dermal denticles with sharp, hooked crowns that point forward and sideways as well as backward....' The liver is massive and helps make the shark neutrally buoyant. When feeding, it cruises near the surface at about two knots, filtering an estimated 2,000 tons of water per hour through its wide open mouth. Its gillrackers have dermal denticles, which filter out plankton.

The Basking Shark is the sole member of its family, Cetorhinidae, and its species, Cetorhinus. These sharks are probably ovoviviparous, i.e., the eggs hatch in the uterus and the pups are born live. The embryos most likely practice uterine cannibalism, feeding on unhatched eggs and their siblings. The pups are thought to be about five and a half feet long at birth. Male Basking Sharks mature between six and seven years of age, when they are about 13 to 16 feet long. They reach a maximum of about 29.5 feet. Females are thought to mature at 26.5 to 32 feet and reach a maximum of about 32 feet. Pregnancies probably last about three and a half years.

The Basking Shark '...is found in subpolar and temperate seas throughout the world, occasionally straying into warmer seas in winter. In North America it ranges in waters off Newfoundland to North Carolina, straying south off Florida and very rarely into the Gulf of Mexico, and from the Gulf of Alaska to Baja California. It is common from Nova Scotia to the Gulf of Maine in summer and in the coastal bays of central and southern California in winter.' (Sharks of North American Waters.) Tom Campbell snorkeled with Basking Sharks off Santa Barbara, California. The waters were plankton laden and the visibility, very poor. The first time a Basking Shark materialized out of the pea soup sea; its enormous mouth fully extended; Tom nearly had heart failure. That encounter, however, produced the wonderful photo that illustrates this article.